Corrugated paperboard having improved wet strength properties



United States Patent 3,467,547 CORRUGATED PAPERBOARD HAVING IM- PROVEDWET STRENGTH PROPERTIES Wildon T. Harvey, Hockessin, Del., and Jay C.Knepper, Jr., Princeton, N.J., assignors to Sun Oil Company,Philadelphia, Pa., a corporation of New Jersey N0 Drawing.Continuation-impart of application Ser. No. 374,835, June 21, 1964. Thisapplication July 6, 1967, Ser. No. 651,365

Int. Cl. D21h 1/22; C09d 3/40 US. Cl. 117-158 2 Claims ABSTRACT OF THEDISCLOSURE An improved wet strength corrugated paperboard compositioncomprising corrugated paperboard impregnated with 25 to 50 weightpercent of a specific petroleum parafiin wax containing 0.1 to 1.0weight percent of a synthetic oil produced by the Friedel-Craftscondensation of aromatic compounds and chlorinated paratfins.

CROSS REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of US. patent application Ser. No. 374,835, filedJune 21, 1964, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the improvement ofthe wet stiffness characteristics of corrugated paperboard boxes. Moreparticularly, this invention relates to an improved corrugatedpaperboard composition which comprises corrugated paperboard impregnatedwith a wax-synthetic oil composition.

For many years corrugated paperboard used in box manufacturing has beenmade with a bituminous layer interposed between intermediate plies ofthe sheet in order to render the corrugated paperboard resistant towater vapor transmission. This has provided paperboard which isrelatively impermeable to water vapor transmission and is inexpensive tomanufacture.

However, this type of corrugated paperboard has been found to be lackingin wet strength properties necessary for stacking, especially when indirect contact with water or when exposed to a moisture-laden atmospherefor prolonged periods of time. This loss of wet strength is attributedto moisture absorbance of the outer unprotected surfaces of thepaperboard.

Waxes have long been used in coating paper, cloths, fibers, food, andcorrugated paperboard products to render them moisture-vapor resistant.However, it has been found that unmodified waxes have a tendency tocrack and peel. This disadvantage is overcome to some degree by additionof polyethylene and other polymers and copolymers. However, the expense,the high temperatures necessary for blending such mixtures, and therelative incompatibility of some of these polymer additives aredisadvantages of these compositions in corrugated paperboardapplications.

DESCRIPTION OF THE INVENTION The present invention provides a paperboardfor use in corrugated boxes which has all of the attractive propertiesof more expensive compositions and yet is relatively inexpensive tomanufacture because of the low concentration of additive necessary toachieve the desired effect. It is among the objects of this invention toprovide an inexpensive wax-synthetic oil composition to rendercorrugated paperboard relatively impermeable to water and therebyimprove the wet strength of the corrugated paper- 3,467,547 PatentedSept. 16, 1969 board. It is among the objects of this invention toprovide an improved corrugated paperboard composition comprising a basecorrugated paperboard impregnated with a thermoplastic homogeneousmixture of 99.0 to 99.9 percent mineral wax and 0.1 to 1.0 percent of asynthetic oil obtained by a Friedel-Crafts condensation of a chlorinatedparaflinic compound and an aromatic compound, with said thermoplasticmixture comprising 25 to 50 weight percent, preferably 35 to 45 percent,of the corrugated paperboard composition.

The synthetic oils used in this invention can be made by variousmethods, but one of the most important methods used heretofore comprisesthe condensation of long-chain aliphatic compounds (e.g., containingmore than 10 carbon atoms) With aromatic ring compounds by means of aFriedel-Crafts catalyst. Among the aliphatic compounds chlorinatedhydrocarbon waxes are preferred, such as chlorinated paraffin wax,although other reactive aliphatic compounds may be used, by which termreactive is meant containing some group such as one or more halogenatoms permitting them to react with an aromatic ring. Such derivativesof petrolatum, fatty acids, fatty alcohols, etc., or other highmolecular weight aliphatic compounds may also be used.

The aromatic compound should preferably be a hydrocarbon such asnaphthalene, anthracene, diphenyl, or the like, or a phenolic compoundsuch as phenol, the naphthols, anthrols, ketones, etc., or amines suchas naphthylamine, aniline, etc. or other aromatic products, such asaromatic esters, ethers, ketones, and the like, as well as methyl,ethyl, and other alkyl derivatives of such aromatic compounds.

It is to be understood that the above-mentioned aromatic hydrocarbonsare set forth only as compounds which may 'be used in the production ofthe aforementioned synthetic oils and that any aromatic compoundcontaining a replaceable hydrogen which will undergo alkylation underthe herein-described process conditions may be used in the production ofsaid synthetic oils.

The condensation of such materials has generally been carried out in thepresence of a Friedel-Crafts catalyst such as aluminum chloride, zincchloride, boron fluoride, etc., preferably in the presence of an inertsolvent such as refined kerosene, tetrachloroethane, etc., and at atemperature varying from about room temperature to about 300 F. andgenerally using proportions of about 2 to 5 mols of the chloro-wax typeof constituent to 1 mol of the aromatic constituent. For example, about10 to 20 parts by weight of chlorinated paraffin wax having about 10 to20 percent chlorine, preferably about 12 to 15 percent chlorine, in thepresence of about 10 to 300 parts, preferably about 25 to parts, byweight of a refined kerosene solvent, and using about 1 to 3 percent byweight of aluminum chloride catalyst based on the weight of thechlorinated paraffin wax can be used.

The reaction is conducted at room temperature for a time period of about24 hours. Near the end of the reaction period, the temperature is raisedto 200 F. until the completion of the reaction. Copious vapors ofhydrochloric acid evolve and are allowed to escape from the treatingvessel during said reaction. Residual catalyst may be hydrolyzed andremoved by washing with Water, alcohol, aqueous caustic soda, or dilutehydrochloric acid, etc., settling and drawing off the resultant sludge,and the desired high molecular weight Friedel-Crafts condensationproduct is recovered from the reaction mass by distillation underreduced pressure such as under vacuum of about 1 to 50 mm. mercuryabsolute pressure, or by fire and steam distillation to a temperature ofabout 600 F.

An example of a synthetic oil used in the embodiment of this inventionis synthesized in the following manner.

A hard paraffin wax having a melting point of 122 to 125 F. ischlorinated by the direct addition of chlorine in the presence of atrace of iodine and at a temperature of about 200 F. The chlorine isblown through the oil for about 24 hours after which the product isfound to contain about 12 percent chlorine which corresponds to apredominate quantity of the monochlor derivative, although there isusually some unchlorinated hydrocarbon. To 90 parts of thischloroparafiin, parts of naphthalene and 10 parts of aluminum chlorideare then added with a sufficient quantity of kerosene to completelydissolve the organic materials. The reaction is carried out at roomtemperature and is found to be substantially complete in about 24 hours,and at this time the temperature is raised gradually to about 200 F.

After the reaction is substantially completed, the product is washedwith dilute aqueous caustic soda to hydrolyze and remove the residualcatalyst. The viscous sludge is permitted to settle, and the oilyFriedel-Crafts condensation product is separated from the reaction massby vacuum distillation at about 50 mm. mercury absolute pressure. Thecondensed product has the following inspection:

The herein-described synthetic oils may be made by the processesoutlined further in detail in U.S. Patent Nos. 1,815,022, 2,352,213,2,410,885, 2,852,557, 2,475,970, 2,882,325, 2,062,354, 2,425,956,2,353,053, 2,339,493, 2,327,525, 2,251,774, 2,141,593, 2,097,127, andothers.

The petroleum paraffin wax which forms a part of the compositions of thepresent invention is characterized as having a melting point in therange of 125 to 132 F., a penetration at 77 F. in the range of 17 to 23,a viscosity at 210 F. in the range of 36 to 39 SUS and a modulus ofrupture at 73 F. of about 270 to 340. Procedures for recovering thisspecific petroleum paraflin wax from petroleum crude oil are disclosedin US. Patents 2,624,501 and 2,906,443.

Generally the improved wet strength corrugated paperboard compositionsof the present invention can be prepared by blending together at atemperature in the range of 180 to 250 F. the paraflin wax and syntheticoil until a homogeneous mixture is obtained. The corrugated paperboardis normally immersed in the wax-oil blend at the blending temperaturefor a period of at least 30 seconds and until the desired amount ofwax-oil blend has impregnated the corrugated paperboard.

The corrugated paperboard is withdrawn from the waxoil blend andpermitted to drain and cool to provide a corrugated paperboardcomposition of enhanced wet stiffness characteristics.

It has been discovered that a thermoplastic composition comprising 0.1to 1.0 weight percent of the abovedescribed synthetic oil and 99.0 to99.9 weight percent of the above-described parafiin wax providescorrugated paperboard with a wet stiffness of at least 280 psi. whenthat corrugated paperboard has been impregnated with 25 to 50 weightpercent of the wax-oil composition. The wet strength improvementincreases with increasing concentrations of added synthetic oil untilthe maximum strength imparted to the corrugated paperboard is reached atabout 0.5 percent of additive.

As one illustration of the present invention the following examples arepresented. The results of preparing compositions as disclosed in theseexamples are presented in the table under the appropriate examplenumber.

4 EXAMPLE I A petroleum parafiin wax prepared in accordance with theprocedures disclosed in US. Patent No. 2,624,501, having the followingcharacteristics:

Melting point F 129 was heated to a temperature of 210 F., and acorrugated board blank was immersed in the molten wax for 30 seconds.The corrugated board was then removed and cooled.

EXAMPLE II To 99.75 parts of a paraflin wax as described in Example Iwas blended at 210 F., 0.25 part of a viscous synthetic oil obtained bya Friedel-Crafts condensation of chlorinated paraflin wax having achlorine content of about 10 to 15 percent with a suitable aromaticcompound such as naphthalene, using about 10 to 15 parts by weight ofnaphthalene to parts by weight of chlornated paraffin wax in thepresence of 0.5 to 15.0 percent of anhydrous aluminum chloride (based onthe total weight of chlorinated wax) and separating supernatant oil fromsettled sludge and distilling ofl? low-boiling constituents from saidsupernatant oil with the resultant residual synthetic oil having thefollowing characteristics:

Gravity A.P.I 23.4 Viscosity index 94 Flash (COC) F 535 Pour F +65Conradson carbon wt. percent 1.9 Viscosity at 210 F. SUS 312 Thissynthetic oil was prepared by Friedel-Crafts condensation described inUS. Patent No. 1,815,022 and others.

A corrugated paperboard blank identical to the blank used in Example Iwas immersed in said wax-synthetic oil mixture for 30 seconds at 210 F.and then removed and cooled.

EXAMPLE III A homogeneous mixture of 99.5 percent parafiin wax asdescribed in Example I and 0.5 percent synthetic oil described inExample II was blended at 210 F., and a corrugated paperboard blankidentical to that used in Example I was immersed in the homogeneousmixture for 30 seconds and removed and cooled.

EXAMPLE IV A homogeneous mixture of 99.25 percent of parafiin wax asdescribed in Example I and 0.75 percent synthetic oil described inExample II was blended at 210 F., and a corrugated paperboard blankidentical to that used in Example I was immersed in said homogeneousmixture for 30 seconds, removed, and cooled.

EXAMPLE V A homogeneous mixture of 99.15 percent paraflin wax asdescribed in Example I and 0.85 percent synthetic oil as described inExample II was blended at 210 F., and a corrugated paperboard blankidentical to that used in Example I was immersed in said homogeneousmixture for 30 seconds, removed, and cooled.

EXAMPLE VI 5 I to VI were all subjected to identical conditions in thefollowing test procedure.

A section of the wax-synthetic oil impregnated corrugated board wassubdivided into three 4 inch by 4 inch sections. These sections wereimmersed in 36 F. water for 2 hours, simulating extremes of highhumidity cold storage. After 2 hours the test specimens were removed,and three 1 inch by 4 inch sections with the 4 inch edge perpendicularto the flutes were cut from the inner part of the specimens. Thestiffness of these sections was measured parallel to the flutes on bothsides using the Tinius-Olsen Stiffness Tester of a 6 inch-pound momentcapacity. The force required in pounds per inch squared to give a 3degree deflection as measured on the stiffness tester was recorded. Theaverage of six measurements was determined and was recorded in thefollowing table. A sample of untreated corrugated board tested under thegiven conditions was too limp to measure. Stiffness was estimated to beapproaching zero.

1 Unmensurable.

The improved wet stiffness characteristics of the corrugated paperboardcompositions of the present invention as illustrated by Examples II toV1 when compared with untreated corrugated board and corrugated boardwhich contains only wax as shown by the blank and Example I respectivelyin the table are clearly evident. Also it can be specifically noted thatan unusually synergistic effect is achieved in the compositions of thepresent invention.

This synergism is apparently the result of a maximum resistance to waterpenetration of the composition in this form, thereby providing asignificant improvement in wet stiffness properties.

We claim:

1. An improved corrugated papenboard having a Wet stiffness of at least280 p.s.i. which comprises corrugated paperboard impregnated with toWeight percent based on the total weight of the paperboard compositionof a thermoplastic composition consisting essentially of (a) 99.0 to99.9 of petroleum parafiin wax characterized as having (1) a meltingpoint in the range of 125-132 F., (2) a viscosity at 210 F. in the rangeof 36-39 SUS, (3) a modulus of rupture at 73 F. in the range of 270-340,and (b) 0.1 to 1.0 Weight percent of a synthetic oil obtained by aFriedel-Crafts condensation of a chlorinated paraffin and an aromaticcompound, said oil being characterized as having (1) an API gravity atF. in the range of 23- 26, (2) a viscosity index in the range of -95,(3) a viscosity at 210 F. in the range of 300-315 SUS, and a ClevelandOpen Cup flash point in the range of 400-600 F. 2. An improvedcorrugated paperboard according to claim 1 containing 35 to 45 weightpercent of the thermoplastic composition.

References Cited UNITED STATES PATENTS 2,085,373 6/1937 Loane et a1.106270 3,023,156 2/1962 Podlipnik 117158 X 3,033,708 5/1962 McKee117-158 X 3,139,353 6/1964 Wommelsdorf et al.117l58X 3,145,118 8/1964Mahoney 117-158 X OTHER REFERENCES Warth, AL, The Chemistry andTechnology of Waxes, 1956, pp. 798, 780-781, 791-792.

WILLIAM D. MARTIN, Primary Examiner M. LUSIGNAN, Assistant Examiner US.Cl. X.R.

